Vermillion Cliffs Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Vermillion Cliffs Observatory clear sky chart from 2005-11-06 to 2024-01-12.

This page is a summary of past forecasts. Even though it's based only on forecasts, some people use these pages as clue to a site's climate. But climate data based on actual observation should be preferred (if you can find it!).

Cloud, Transparency and Seeing forecasts are summarized individually. But because good observing conditions require a combination of minimum cloud cover, transparency and seeing, the individual forecast summaries can be difficult to interpret. The observing conditions section counts the combinations of conditions needed for common types of astronomical observation.

Observing Conditions

The following tables count the occurrence of the combinations of forecast and darkness conditions needed for different observations. Conditions are rated by by what percentage of the hours the observation would likely be attempted are usable.
Observation TypeMinimum conditions for hour to be usableOut of hours
Clear of CloudsTransparencySeeingSky Brightness
Planetary:50%(no limit)Average(no limit)Nighttime Hours
Deep Sky:70%Average(no limit)5.9Nighttime Hours
CCD Imaging:70%Below AveragePoor(no limit)Nighttime Hours

Percentages are of nighttime hours per month, or per year, when a particular observing conditions was met. Deep Sky percentages never exceed 50% because the moon is up half the time. Deep sky percentages are much lower for charts at high latitudes because of fewer dark hours in the summer.

Overall

PlanetaryData
Pts
Deep Sky
Max 60%
Data
Pts
Both Planetary and Deep Sky
Max 60%
Data
Pts
Either Planetary or Deep SkyData
Pts
CCD ImagingData
Pts
Night
66%
24019
23%
74357
18%
23965
72%
23965
24%
48477

By Month

MonthDays of MonthPlanetaryData
Pts
Deep Sky
Max 60%
Data
Pts
Both Planetary and Deep Sky
Max 60%
Data
Pts
Either Planetary or Deep SkyData
Pts
CCD ImagingData
Pts
January1st to 10thNight
57%
756
22%
2457
18%
756
64%
756
21%
1640
January11th to 20thNight
63%
728
21%
2366
19%
728
68%
728
20%
1607
January21st to endNight
59%
792
23%
2574
18%
792
67%
792
20%
1768
February1st to 10thNight
59%
720
19%
2326
14%
720
67%
720
23%
1510
February11th to 20thNight
57%
700
20%
2099
15%
700
66%
700
23%
1425
February21st to endNight
51%
592
23%
1776
17%
592
60%
592
20%
1249
March1st to 10thNight
56%
720
21%
2032
15%
720
64%
720
23%
1397
March11th to 20thNight
60%
720
25%
1980
18%
720
66%
720
24%
1374
March21st to endNight
55%
792
21%
2178
11%
792
64%
792
24%
1522
April1st to 10thNight
52%
720
20%
1980
9%
720
60%
720
26%
1345
April11th to 20thNight
54%
591
28%
1722
15%
591
65%
591
26%
1101
April21st to endNight
55%
540
27%
1620
16%
540
65%
540
26%
1030
May1st to 10thNight
57%
540
24%
1620
14%
540
65%
540
27%
1021
May11th to 20thNight
66%
531
27%
1595
20%
531
71%
531
27%
1011
May21st to endNight
61%
583
24%
1746
15%
582
68%
582
26%
1102
June1st to 10thNight
71%
540
23%
1620
19%
540
74%
540
30%
993
June11th to 20thNight
70%
540
25%
1620
22%
540
73%
540
30%
993
June21st to endNight
79%
540
24%
1620
22%
540
81%
540
31%
985
July1st to 10thNight
83%
525
19%
1575
17%
525
83%
525
27%
998
July11th to 20thNight
81%
522
19%
1566
17%
522
81%
522
21%
1081
July21st to endNight
79%
591
16%
1674
13%
558
79%
558
18%
1204
August1st to 10thNight
82%
537
23%
1602
19%
534
82%
534
28%
1014
August11th to 20thNight
84%
534
27%
1602
24%
534
85%
534
25%
1044
August21st to endNight
82%
661
24%
1885
20%
661
82%
661
27%
1244
September1st to 10thNight
82%
720
22%
1980
18%
720
84%
720
28%
1317
September11th to 20thNight
82%
720
28%
1980
24%
720
84%
720
30%
1287
September21st to endNight
79%
720
29%
1980
21%
720
83%
720
34%
1229
October1st to 10thNight
70%
720
23%
2011
17%
720
74%
720
27%
1345
October11th to 20thNight
74%
720
30%
2160
25%
720
79%
720
32%
1318
October21st to endNight
70%
792
28%
2376
21%
792
76%
792
30%
1473
November1st to 10thNight
75%
740
22%
2341
18%
740
80%
740
23%
1541
November11th to 20thNight
72%
760
27%
2470
23%
760
79%
760
26%
1533
November21st to endNight
64%
760
23%
2470
21%
760
70%
760
24%
1589
December1st to 10thNight
61%
760
21%
2470
18%
760
67%
760
22%
1652
December11th to 20thNight
58%
759
21%
2913
16%
758
65%
758
17%
1980
December21st to endNight
51%
833
11%
4371
14%
817
57%
817
12%
2555

Individual Forecasts

The length of each colored bar in the "occurrence of each Forecast" column is proportional to the number of times the chart forecast that color. The percentages are of the total number of hours per month, or per year, with a particular forecast. The colors as the same as those used in clear sky charts.

Note: Transparency probabilities are only counted for those hours that have 30% or less cloud cover. Seeing probabilities are only counted for those hours that have 80% or less cloud cover. If that's too tricky, try Observing Conditions instead.

Overall

Occurrence of each ForecastData
Points
Cloud CoverDay
431332445%7%64%
74926
Night
431332345%7%65%
74840
TransparencyDay
13%36%413%18%15%
74653
Night
13%36%5%13%19%14%
74635
SeeingDay
6%10%26%33%18%6%
13790
Night
5%420%41%27%4
24032

By Month

Percentage Cloud Cover SW (2006-)
Color Meanings:
Overcast 90% covered 80% covered 70% covered 60% covered 50% covered 40% covered 30% covered 20% covered 10% covered Clear
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 10thDay
6%5%15%433348%59%
1708
11th to 20thDay
441322335%7%64%
1633
21st to endDay
7%5%12324348%59%
1782
February1st to 10thDay
35%2331345%8%64%
1633
11th to 20thDay
5%5%2432346%7%59%
1750
21st to endDay
5%7%25%42435%6%57%
1480
March1st to 10thDay
6%5%2332445%6%59%
1927
11th to 20thDay
36%2332446%7%59%
1980
21st to endDay
5%5%23334448%59%
2178
April1st to 10thDay
332342446%7%62%
1980
11th to 20thDay
3413313447%66%
2181
21st to endDay
332332445%6%67%
2340
May1st to 10thDay
43135%2345%6%63%
2340
11th to 20thDay
331232446%7%65%
2301
21st to endDay
4313323346%67%
2530
June1st to 10thDay
1112213337%76%
2340
11th to 20thDay
1111212335%78%
2340
21st to endDay
1112213345%77%
2340
July1st to 10thDay
32133345%6%6%64%
2340
11th to 20thDay
32145%45%6%7%9%54%
2340
21st to endDay
5%326%6%48%7%8%10%41%
2545
August1st to 10thDay
4213435%5%6%7%59%
2328
11th to 20thDay
42135%3446%8%59%
2299
21st to endDay
432343446%7%61%
2466
September1st to 10thDay
321332446%6%65%
1980
11th to 20thDay
3212222335%75%
1980
21st to endDay
3212222337%73%
1980
October1st to 10thDay
5%213323345%68%
1947
11th to 20thDay
211222223479%
1800
21st to endDay
2112312235%77%
1980
November1st to 10thDay
2312213246%74%
1733
11th to 20thDay
222213345%75%
1710
21st to endDay
5%413313446%67%
1710
December1st to 10thDay
45%14424346%63%
1710
11th to 20thDay
7%6%35%4345%6%8%51%
2169
21st to endDay
6%6%24435%5%6%8%52%
3146
January1st to 10thNight
7%5%1332335%7%61%
2457
11th to 20thNight
5%42432335%6%63%
2366
21st to endNight
6%6%2433445%7%57%
2574
February1st to 10thNight
45%12323347%66%
2326
11th to 20thNight
45%2332345%6%62%
2098
21st to endNight
5%8%34323447%58%
1776
March1st to 10thNight
6%5%134235%5%8%58%
2032
11th to 20thNight
6%5%23323349%59%
1980
21st to endNight
343332436%7%62%
2178
April1st to 10thNight
4323323445%66%
1980
11th to 20thNight
331222345%8%67%
1722
21st to endNight
421332345%7%67%
1620
May1st to 10thNight
421331345%7%66%
1620
11th to 20thNight
2212313346%73%
1594
21st to endNight
4212323346%70%
1746
June1st to 10thNight
212212345%78%
1620
11th to 20thNight
112212335%78%
1620
21st to endNight
112312336%78%
1620
July1st to 10thNight
221242446%7%65%
1620
11th to 20thNight
3424435%46%8%57%
1620
21st to endNight
44246%45%6%8%12%46%
1773
August1st to 10thNight
221342346%7%64%
1611
11th to 20thNight
221432346%9%64%
1602
21st to endNight
321342345%6%66%
1885
September1st to 10thNight
421332346%7%66%
1980
11th to 20thNight
221221335%5%74%
1980
21st to endNight
2211223335%77%
1980
October1st to 10thNight
4323323346%68%
2011
11th to 20thNight
321221223478%
2160
21st to endNight
3212222346%75%
2376
November1st to 10thNight
2212223347%72%
2341
11th to 20thNight
2112222346%75%
2470
21st to endNight
4313322236%69%
2470
December1st to 10thNight
6%5%23323347%62%
2470
11th to 20thNight
7%5%243235%5%9%54%
3041
21st to endNight
6%6%2443445%7%54%
4521

Transparency (when cloud cover <= 30%)
Color Meanings:
Too cloudy to forecast Poor Below Average Average Above average Transparent
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 10thDay
13%39%8%20%17%2
1709
11th to 20thDay
11%40%5%21%19%4
1633
21st to endDay
18%38%8%20%13%4
1782
February1st to 10thDay
13%36%8%14%22%7%
1633
11th to 20thDay
16%36%419%16%10%
1760
21st to endDay
18%36%6%14%20%7%
1480
March1st to 10thDay
17%36%316%22%6%
1927
11th to 20thDay
17%36%419%18%5%
1980
21st to endDay
17%37%419%17%6%
2178
April1st to 10thDay
13%36%314%21%13%
1980
11th to 20thDay
12%35%315%21%15%
2184
21st to endDay
10%36%213%26%14%
2340
May1st to 10thDay
11%36%38%25%17%
2340
11th to 20thDay
10%37%211%24%16%
2304
21st to endDay
9%36%211%22%19%
2530
June1st to 10thDay
8%36%28%22%24%
2340
11th to 20thDay
7%36%1414%38%
2340
21st to endDay
8%35%1414%38%
2340
July1st to 10thDay
11%38%35%11%32%
2276
11th to 20thDay
17%38%5%10%14%15%
2271
21st to endDay
24%39%9%13%9%6%
2404
August1st to 10thDay
15%36%6%11%9%24%
2313
11th to 20thDay
16%35%5%11%12%21%
2299
21st to endDay
15%36%38%18%19%
2466
September1st to 10thDay
15%36%47%11%27%
1980
11th to 20thDay
11%36%411%14%24%
1980
21st to endDay
8%36%27%21%27%
1980
October1st to 10thDay
13%37%314%19%15%
1947
11th to 20thDay
6%35%210%24%23%
1800
21st to endDay
7%36%311%29%14%
1980
November1st to 10thDay
10%39%418%21%8%
1733
11th to 20thDay
8%39%6%16%23%9%
1710
21st to endDay
10%39%415%24%9%
1710
December1st to 10thDay
13%39%7%17%17%7%
1710
11th to 20thDay
24%34%8%19%13%2
2168
21st to endDay
24%25%10%16%20%5%
3146
January1st to 10thNight
14%38%6%22%19%2
2457
11th to 20thNight
14%40%5%17%19%6%
2366
21st to endNight
17%38%7%19%15%4
2574
February1st to 10thNight
14%36%6%17%21%7%
2326
11th to 20thNight
15%37%5%15%18%11%
2099
21st to endNight
18%37%414%19%7%
1776
March1st to 10thNight
15%36%417%20%7%
2032
11th to 20thNight
15%37%419%19%6%
1980
21st to endNight
16%36%5%20%15%8%
2178
April1st to 10thNight
13%36%315%20%13%
1980
11th to 20thNight
11%35%415%20%15%
1722
21st to endNight
9%36%312%27%13%
1620
May1st to 10thNight
9%36%39%26%18%
1620
11th to 20thNight
8%37%211%23%19%
1595
21st to endNight
9%36%39%23%20%
1746
June1st to 10thNight
7%35%29%23%24%
1620
11th to 20thNight
8%35%16%12%39%
1620
21st to endNight
6%35%1414%39%
1620
July1st to 10thNight
8%38%46%10%33%
1575
11th to 20thNight
17%37%410%12%19%
1566
21st to endNight
18%40%10%15%10%6%
1674
August1st to 10thNight
10%35%7%12%12%24%
1602
11th to 20thNight
13%35%5%10%15%22%
1602
21st to endNight
12%36%49%16%24%
1885
September1st to 10thNight
11%36%49%13%26%
1980
11th to 20thNight
8%37%5%12%14%25%
1980
21st to endNight
5%35%28%22%28%
1980
October1st to 10thNight
12%36%314%19%15%
2011
11th to 20thNight
7%35%39%24%23%
2160
21st to endNight
7%36%410%27%17%
2376
November1st to 10thNight
10%40%416%20%10%
2341
11th to 20thNight
7%39%5%14%26%9%
2470
21st to endNight
10%38%411%26%11%
2470
December1st to 10thNight
13%39%6%17%17%8%
2470
11th to 20thNight
21%33%8%20%17%1
3041
21st to endNight
24%26%10%13%19%8%
4521

Seeing (when cloud cover <= 80%)
Color Meanings:
Too cloudy to forecast Bad 1/5 Poor 2/5 Average 3/5 Good 4/5 Excellent 5/5
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 10thDay
14%7%36%35%7%1
270
11th to 20thDay
9%9%36%29%15%1
245
21st to endDay
9%5%27%37%18%4
264
February1st to 10thDay
8%9%31%32%17%4
253
11th to 20thDay
12%13%37%27%10%
415
21st to endDay
7%21%37%23%10%1
346
March1st to 10thDay
11%17%33%27%10%2
420
11th to 20thDay
7%17%30%30%12%3
420
21st to endDay
11%20%36%26%6%1
462
April1st to 10thDay
7%18%34%22%14%4
420
11th to 20thDay
10%22%32%24%11%1
412
21st to endDay
8%19%29%28%12%3
420
May1st to 10thDay
8%16%35%28%11%3
423
11th to 20thDay
6%13%26%32%17%5%
448
21st to endDay
11%14%27%27%15%6%
485
June1st to 10thDay
47%28%38%16%7%
450
11th to 20thDay
311%27%36%16%8%
450
21st to endDay
2427%40%20%7%
450
July1st to 10thDay
1221%38%27%10%
446
11th to 20thDay
2214%38%28%15%
444
21st to endDay
319%40%31%15%
487
August1st to 10thDay
4318%38%24%12%
447
11th to 20thDay
4318%39%24%13%
437
21st to endDay
3318%36%26%14%
495
September1st to 10thDay
4318%34%28%13%
450
11th to 20thDay
46%24%37%23%7%
450
21st to endDay
47%23%31%26%8%
450
October1st to 10thDay
7%10%25%31%19%9%
417
11th to 20thDay
29%22%34%24%9%
270
21st to endDay
5%8%27%34%24%2
297
November1st to 10thDay
5%11%21%36%22%6%
270
11th to 20thDay
47%27%40%16%7%
270
21st to endDay
9%8%27%37%15%4
270
December1st to 10thDay
6%8%30%35%17%4
270
11th to 20thDay
5%8%34%37%14%2
270
21st to endDay
16%10%28%33%12%
297
January1st to 10thNight
9%425%40%17%4
760
11th to 20thNight
7%422%44%20%4
728
21st to endNight
10%323%40%20%4
792
February1st to 10thNight
6%327%42%18%3
720
11th to 20thNight
7%5%28%43%15%2
704
21st to endNight
9%5%30%39%16%1
592
March1st to 10thNight
8%9%23%41%16%2
720
11th to 20thNight
7%6%22%38%24%3
720
21st to endNight
5%7%28%40%18%2
792
April1st to 10thNight
5%8%31%38%17%2
720
11th to 20thNight
38%32%39%16%2
591
21st to endNight
5%10%27%39%16%3
540
May1st to 10thNight
5%429%46%14%2
540
11th to 20thNight
35%23%39%28%2
531
21st to endNight
47%23%41%22%3
584
June1st to 10thNight
2420%45%27%2
540
11th to 20thNight
15%20%46%26%2
540
21st to endNight
1214%47%35%1
540
July1st to 10thNight
217%41%45%3
525
11th to 20thNight
416%37%48%5%
522
21st to endNight
5%1430%54%6%
591
August1st to 10thNight
315%38%50%3
537
11th to 20thNight
215%41%48%4
534
21st to endNight
415%34%48%8%
661
September1st to 10thNight
427%33%49%6%
720
11th to 20thNight
319%42%38%8%
720
21st to endNight
3313%36%38%8%
720
October1st to 10thNight
5%317%47%25%3
720
11th to 20thNight
3218%43%27%8%
720
21st to endNight
3221%39%28%7%
792
November1st to 10thNight
3217%48%25%6%
740
11th to 20thNight
2220%47%23%5%
760
21st to endNight
6%322%42%23%4
760
December1st to 10thNight
9%423%42%20%3
760
11th to 20thNight
9%326%41%19%2
760
21st to endNight
14%425%40%16%1
836
Page generated at 2024-01-09 14:24:26. Version ac07

Copyright 2024 Attilla Danko


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